Breast cancers in African American (AA) women are characterized by earlier onset, higher aggressiveness, more extensive metastases, and increased mortality rates compared to those in European American (EA) women. This breast cancer-related health disparity is partly due to the fact that AA women are more likely than EA women to develop a particularly aggressive breast cancer subtype, called Triple-Negative Breast Cancer (TNBC). TNBC is characterized by fast progression to metastasis and high mortality rates. Furthermore, there are no targeted therapies for TNBC. Critical barriers to progress in improving outcomes for AA TNBC patients are (i) a lack of reliable risk-predictive biomarkers that can identify TNBCs at high risk of progressing rapidly to metastatic disease, and (ii) targeted therapies for TNBCs. Since tumor biology between AA and EA women with TNBC can vary greatly, the optimal way to combat TNBC may differ between AA and EA patients. Thus, it is critical to identify key biomarkers that may have special therapeutic and prognostic value within certain ethnic subgroups. We recently found that AA TNBC patients were ~3 times as likely as EA TNBC patients to have high nuclear levels of HSET, a centrosome-clustering kinesin. We found that higher nuclear HSET levels were also associated with more aggressive tumor features and decreased metastasis-free survival. As a result, nuclear HSET may be a racial disparity biomarker in TNBC. Furthermore, HSET may be a valuable target to suppress metastasis because we found that TNBC cell migration was inhibited by HSET knockdown. Overexpression of Npap60L, a nucleoporin isoform, is known to suppress nuclear import. In a search of publically-available gene expression databases, we found that AA TNBCs have lower Npap60L levels than EA TNBCs. Therefore, we hypothesize that low Npap60L levels in AA TNBCs promotes nuclear accumulation of HSET. Our novel paradigm that ethnic differences in nuclear transport pathways promote different subcellular localization of HSET, a key mediator of metastasis, is a groundbreaking conceptual advancement. It holds translational promise not only in metastatic risk prediction but also in providing an anti- metastatic therapeutic target for TNBC patients with high nuclear HSET. AIM 1 will establish nuclear HSET as a racial disparity biomarker by evaluating its nuclear expression as a predictor of a) metastasis, b) poor progression-free survival, and c) poor overall survival in AA TNBC patients. AIM 2 will test whether racial differences in the levels of a nucleoporin protein (Npap60L) involved in nuclear import promotes nuclear retention of HSET in AA TNBCs. The overall impact of this project will be to validate HSET as a racial disparity biomarker and mechanistically define the Npap60L-HSET axis as a new pathway that can be targeted to thwart metastatic onset in AA TNBC patients and alleviate ethnic breast cancer-related health disparity.